Soil organic and inorganic carbon contents of landscape units in Belgium derived using data from 1950 to 1970

Belgium's soil survey data collected between 1950 and 1970 (pre-Kyoto Protocol) contain more than 13000 geo-referenced soil profile descriptions, which allow the computation of a spatially distributed baseline carbon content for incremental soil depths, based on soil/land-use combinations (landscape units) and multiple matching soil profile observations. The results show that the soil organic carbon (SOC) and soil inorganic carbon (SIOC) contents of many landscape units do not differ significantly. However, landscape units under forest and grassland tend to contain more carbon. The same is true for landscape units on poorly drained and/or clayey soils, podzols or anthropogenic soils. The change of the SOC in the upper 100 cm of mineral soil follows a logarithmic decline with increasing depth, useful for the extrapolation of SOC of surface layers to deeper layers. SIOC values are strongly related to the geological soil characteristics and increase linearly with depth. Integrating the mean SOC and SIOC content of landscape units over the Belgian territory results in a total soil carbon stock of 303 MtC in the upper 100 cm layer. Ectorganic horizons contain 35 MtC and mineral soil contains 245 MtC in organic form and 23 MtC in inorganic form. These results are shown to be consistent with an independent set of SOC measurements on 3134 surface samples.